This invention relates to composite shafts, and more particularly to a composite shaft end assembly, composite shafts formed therewith, and a method of forming composite shafts formed therewith.
Composite shafts are used to transmit rotational power between driver and driven rotating devices, and typically include a fibrous composite tube having opposing ends. An end assembly in each tube end connects to one of the rotating devices. Each end assembly has one end fixed to the composite tube and an opposing end adapted to connect to the rotating device. The end assemblies are formed from metal in order to withstand the forces exerted thereon by the rotating devices and for welding a fixture thereto.
Transmission of large torque loads across a joint between the fiber reinforced composite tube and the metal end assembly is not easy due to the different torsional stiffness in the materials and varying thermal coefficients. One known method includes using an epoxy adhesive to bond a metal fitting inserted into the composite tube to the composite tube, and then drilling holes through the composite material and fitting. Rivets inserted through the holes fix the end assembly to the metal fitting, and thus the composite tube. Another known method for joining a metal end assembly to a composite tube uses an interference fit compression joint, such as disclosed in U.S. Pat. No. 4,451,245, which clamps onto the end of the composite tube. Both of these methods are expensive to implement because of the tight tolerances of the metal parts that are required for the end assembly.
Other methods for transmitting torque loads across a metal-composite joint are also known that require special formation of the composite tube ends. For example, in one known method, the composite tube is formed around the end assemblies and then cured to bond the composite tube to the end assemblies. Keys and slots formed in the end assembly or tubes can be provided to rotatably fix the end assembly to the tube if the bond between the metal end assembly and composite tube fails. Unfortunately, once made, the length of these composite shafts cannot be changed to fit a particular application. As a result, an inventory of assembled composite shafts having standard lengths can be maintained. However, a custom shaft must be ordered and fabricated if a non-standard length is required.